Line Relay Modeling

See Also

Transmission Line Relay Models in Simulator are assigned directly to a particular branch in Simulator. Many line relays will also apply to specific end of the branch. When a relay type requires the assignment of a specific end of the branch, there will be a field Device Location which can be set to either From or To. The Device Location also becomes one of the key fields for that type of line relay Key Fields. The Device Location can also be specified on the transient stability tab of the branch dialog by checking the box Device is at From End of Line (otherwise at To End). The end specified by the Device Location is referred to as the "Relay End", while the other is referred to as the "Other End".

For most types of relays, only one of that type may be assigned to each end of the branch. Thus you could only have two ZLIN1 relays assigned to a branch with one assigned to the From location and the other to the To. Some relays however allow multiple relays of the same type to be assigned to the same end of a branch (for example OOSLEN). For these relay types, there will be an another field Device ID to which a two character id is assigned. Again, the Device ID will be treated as a Key Field for that type of relay.

Details about specific line relays are contained in the Transient Stability Block Diagram PDF document, so look there for more information.

Special User Interface Features for Time Inverse Over-Current Relays

On the branch dialog's Transient Stability Tab, for relays which represent an impedance-based distance relay, there will also be an extra button Show Relay Zones available to help you visualize the Time To Close or Time to Reset curve for the relay. These relay types include LOCTI, TIOCR1, and TIOCRS.

Special User Interface Features for Impedance-Based Distance Relays

Finally, in the Transient Stability Model Explorer, for Line Relay Models there are three extra columns showing the Forward Reach Percentage for Zones 1, 2, and 3.

If these are not related to the particular line relay, then the fields will appear blank. For those relays for which this is relevant, the forward reach impedance (typically denoted as Rf1, Rf2, etc...) will go through the following calculation to obtain a percentage with the value shown in the respective field.

Note that these percentages and the Rforward points are also marked on the plot created when clicking the Show Relay Zones buttons mentioned above.

Also for impedance-based distance relays for which a "Far Bus" is specified (such as ZLIN1, ZQLIN1, ZPOTT, etc...), then Simulator will automatically start at the Device Location bus of the branch and do a topology search of the network to find the series of branches that get to the "Far Bus". The Reach Percentage is then based on the sum of branch impedances on the series path found. In addition the Show Relay Zones feature will include additional information about the intermediate points found as this series path is traversed.

If any loops are found while doing this search that circle back to the Device Location bus, then this search is aborted and the LineR and LineX of the branch to which the relay is assigned is used as normal. For impedance-based relays that do not have a Far Bus, but do specify transfer trip lines (such as DISTR1), then Simulator will do a similar search to find the series path by assuming that the last branch in this series path is the first transfer trip line.

The following image is what you'll see when a series of two branches are described.